Hi
Does anyone have a scientific explanation? How to decide on the optimal point? when the wind blows stronger - take it forward, backward, or leave it in its place?
I look for an explanation rather than self experience...

IZZY

Refer to the laws of levers, fluid dynamics and Elmo's Murphy's laws.

If you want the nose up, earlier planing, or more maneouvreability bring it back. If you want the nose down, more directional stability, shift it forward.[Assuming you don't change anything else at the same time]

In moving the mast foot, as well as changing the lever arm of the mast foot on the board, you alter the rake angle of the mast, and as a result, the sail. This moves the centre of effort from the sail in relation to yourself, and in relation to the lift provided by the fin, which alters your sailing experience significantly.

Then you shift your boom up or down, and you've just introduced a further variable.. On a wave board, you can also shift your fin, again altering the behaviour of the setup. Then there are factors like downhaul tension, and outhaul tension, harness line position and length, footstrap placement...

So, there are many variables in the equation.. There is a scientifc explanation, but it would be long, convoluted, and extremely difficult to evaluate given that sea state, wind conditions, and rider skill and technique are so variable.

The article elmo posted is a good guide. Most of the guys I know have a favorite setting for their mast bases, and tune the rest of the setup around it. But that's all 'self experience'.

As nice as it would be to have a formula to give you the answer, in the end whether a particular setup works for you or not is very subjective (unless maybe you're into speed sailing, and can see a difference in your GPS speed)

Ultimately, it is up to you to decide, and that is something that really only comes with experience. As with all experiments though, I recommend changing only one part of the equation at a time to really observe the effects. Start with a recommended configuration, and then customise it to suit yourself from there.

nobody said...

As per my usual interaction with 555, I disagree with the following:

I believe by moving the mast foot back you increase nose lift which reduces early planing as you should be trying to flatten the board to get it going.

An interesting preconception nobody! Whatever 555 says [that is in my depth], I will disagree with!

You are correct, a flat board (planing surface parallel with the water surface) is the goal. But a board that has it's nose or rocker plastered firmly onto/into the water by a mast-foot that is "too far" forward will take more effort to get onto the plane, and not be as pleasant to ride as it could be once planing.

So, if planing seems like it should be possible, but isn't happening, you could try shifting the mastfoot back a bit, and that may help. Try it and see!

NB: Simon Bornhoft also mentions this in the article that Elmo posted.. right down near the end in the part about when to consider shifting your mastfoot back: "If the board feels like it's ploughing on the nose and won't really release, accelerate or ride over chop smoothly". Feel free to disagree though - Simon's not that experienced http://www.boards.co.uk/magazine/editorial_team.asp?ID_P=12

A rough rule of thumb I use is that with a smaller sail, the mast foot is further back. I figure the centre of effort on the sail is further forward on a small sail and so to get it more balanced in respect to where I am standing on the board, the sail must be brought back. Does this make sense?

elmo said...

http://www.boards.co.uk/articles/index.asp?ID_A=191&article_type=25

Thanks Elmo mate, that was a very good read and for me I need to have the mast base further forward so from there I can start to tune the rig, its a bit like castor and camber on a car except in reverse, in regards to how it will effect turn in, mast base further forward and the board becomes more stable and but has less turning in ability, further back and the board becomes faster and turns into gybe or off the bottom better.

I said a "BIT" like

Thanks again and good thread izzykatz

all the way forward = go to china

all tha way back = got to the moon

nebbian said...

MintoxGT wrote:
its a bit like castor and camber on a car except in reverse, in regards to how it will effect turn in, mast base further forward and the board becomes more stable and but has less turning in ability, further back and the board becomes faster and turns into gybe or off the bottom better.

THAT's the first explanation I've seen that makes sense!

Just got to try it now...

Thanks Mr T

No worries Nebbs, finally after 4 years I actually have contributed in helping someone about windsurfing on SB

When you try the changes could you give feedback, I reckon that with your experience you should really notice the effects, it would be interesting for me to hear how you went.

Cheers Mr T

I just read an article of Cribbies in the latest Windsurf (May issue) about rigging for marathon downwinders. Amongst other things he recommends pushing the mast foot forward a smidge (maybe a 1/4 from the front) to hold the nose down. That strikes me as counter-intuitive because on downwinders I'm always struggling to hold the nose up. I'll have to try his setup and see.

The check list is
1) Front straps outboard and one hole back
2) Single back strap in forward holes
3) Largish freeride board with smallish fin
4) Normal (i.e. high) boom
5) Mast foot forward
6) Waist harness

Note this is for endurance sailing downwind not speed sailing. Its contrived to allow an upright stance with straight legs.